The problem with manufacturers specs is that they don't all adhere to the same standard, as for musical instrument speakers there is no industry wide standard. The quoted '50Hz to 20kHz' of the GK, for instance, doesn't tell you how many dB down the reponse is from average at either 50Hz or 20kHz. If it's -3dB, (as would usually be the case for high fidelity speakers) that's quite good. I can guarantee you that it is not -3dB, as no 15 inch speaker is capable of that performance. For that matter, no 15 inch speaker is capable of 106dB/SPL either unless horn loaded, so that figure is either a mis-statement by the poster or bull****by GK.
The aforementioned "David Eden" also makes claims for bandwidth and SPL which defy logic, as there are no drivers made capable of the performance Eden claims from the cabinet design that they use.
The only way to make a real comparison is to see an actual measured response chart. Good luck on that one.